Apparatus for low power tensioned winding of concrete articles



June 1956 J. M. CROM, JR 2,749,054

APPARATUS FOR LOW POWER TENSIONED WINDING OF CONCRETE ARTICLES Filed May21, 1952 4 Sheets-Sneet 1 INVENTOR Jam/1mm Jr:

ATTORNEYS June 5, 1956 2,749,054

J. M. CROM, JR APPARATUS FOR LOW POWER TENSIONED WINDING OF CONCRETEARTICLES Filed May 21. 1952 4 Sheets-Sneet 2 ATTORNEYS un 1956 J. CROM,JR 2,749,054

APPARATUS FOR LOW POWER TENSIONED WINDING OF CQNCRETE ARTICLES Filed May21. 1952 4 Sheets-Sneet I5 J n 5, 9 .1. M. CROM. JR

APPARATUS FOR LOW POWER TENSIONED WINDING OF CONCRETE ARTICLES 4Sheets$neet Filed May 21, 1952 Jain/M 61mm ab:

ATR WNFYS APPARATUS FOR LOW POWER TENSIONED WIND- ING OF CONCRETEARTICLES This invention relates to an apparatus for continuouslyprestressing concrete articles.

Heretofore in the prior art, methods and apparatus have been advancedfor the continuous prestressing of concrete articles. These methods andapparatus, while producing the desired result, have, nevertheless, beenextremely costly by reason of the equipment involved and have alsorequired the consumption of considerable power. In some of these methodsand apparatus where wire has been continuously tensioned while payingout from a source of supply to effect prestressing, the load whichcaused tension has had to act over the entire length of the wire. Thework done by these methods and apparatus, therefore, is equal to theproduct of the length of the wire and the load applied. This results inthe expenditure' of a large amount of work.

In contradistinction to the above methods and apparatus of continuouslyprestressing, the linear prestressing of beams and the like bytensioning wires is generally affected by stressing from one end only.The load in this instance acts only over a relatively short length toproduce the stretch desired. The Work done, therefore, is equal to theproduct of the change in length of the wire and the mean load applied.

It follows from the foregoing then that the theoretical work necessaryto stress wire as illustrated by the linear prestressing method isconsiderably less than when the load acts over the entire length ofwire, as is usually the casein continuous prestressing methods andapparatus.

By the present invention, an apparatus for continuously prestressingpipes, tanks, roads, or the like is advanced which provides a means forprestressing that does not require the load to act over the entirelength of the wire.

It is an object of this invention to provide an apparatus forcontinuously prestressing concrete bodies that results in expending lesswork to effect the prestressing than methods which have heretofore beenavailable.

It is another object of this invention to provide an apparatus forcontinuously prestressing that will be more economical and eflicientthan apparatuses which have heretofore been available.

It is another object of this invention to provide an apparatus forcontinuously stressing wires which involves the consumption of lesspower and by which apparatus wires can be stressed with greater facilityand speed than has heretofore been available.

Other objects and advantages of the present invention will becomeapparent from a study of the following specification when considered inconjunction with the drawings, in which:

Figure 1 is a plan view showing the method of this invention as appliedto the continuous prestressing of concrete pipes;

Figure 2 is a vertical section of the clutch assembly taken along line22 of Figure 1;

nited States Patent Figure 3 is a vertical section of the clutchassembly taken along line 3-3 of Figure 2;

Figure 4 is a schematic representation illustrating the theory of thisinvention;

Figure 5 is a view in side elevation of a modification of this inventionshowing the method applied to the continuous prestressing of concretepipes;

Figure 6 is a plan view of the modification showniu Figure 5;

Figure 7. is a schematic representation of the modification shown inFigure 5;

Figure 8 is a view in side elevation of a further modification showingthe method applied to the continuous prestressing of concrete pipeswhile in a vertical position;

Figure 9 is a view in side elevation of a further modification showingthe method applied to the continuous prestressing of concrete tanks;

Figure 10 is a plan view of the modification shown in Figure 9;

Figure 11 is a view in side elevation of a further modification showingthe method applied to the continuous prestressingof concrete roads; and

Figure 12 is a view in front elevation of the modification shown in Fig.11.

Before referring to the drawings for a detailed description of theinvention, Figures 1 and 4 will be discussed to enable a clearunderstanding of the theory by which this invention operates. As can beseen in Figure l, the wire 20 which is ultimately to be wound on aconcrete pipe 21 is first wound several turns around a tapered brakingdrum 22. Wire 20 is wound on drum 22 with a small initial back-tensionto prevent the wire from slipping uncontrollably around tapered drum 22.This backtension can be produced by passing the wire initially through asmall draft die, lightly gripping wooden blocks,

wheels that cold work the wire, drive an electric generator, orhydraulic pump or any such similar device. Both the pipe 21 and the drum22 are mounted upon a common shaft 23 to which power is supplied bymeans of an electric motor 24. The drum diameter is slightly smallerthan the pipe diameter. One rotation of the pipe 21 will require alength of wire equal to the pipe circumference. However, one rotation ofthe pipe results in wire being payed out from the drum-22 in a lengthequal to the circumference of the drum. Inasmuch as the drum is ofsmaller diameter the amount of wire released by the drum is insufiicientto go around the pipe. Consequently the wire 20 must be stretched if itis to go around the pipe 21. Therefore, by controlling. the relativediameter of the drum and pipe it is possible to obtain the exact desiredstress in the wire. Stated in another way, for a pipe of a givendiameter there is theoretically a corresponding drum of smaller diameterthat will cooperate with the pipe to produce the proper stress in thewire. As the variables of the problem are the diameters of the pipe anddrum and the stress in the wire, the establishment of any two variableswill determine the third. In Figure 4 is shown a schematicrepresentation of the forces produced by the tensioned wire and theirdirection. Since the tensioned wire is common to both the drum and thepipe, the forces exerted on the wire with respect to the drum and pipeare equal and in a direction opposed to the tension in the wire. HenceTa, the force exerted on the drum is equal and opposite to Tb, the forceexerted on the pipe.

The wire is-wound on the drum and pipe so that torque raTrz opposestorque rbTb. Consequently, the force required to turn the pipe is equalto the torque of (rb-ra) Ta. This force is greatly less than that ofprevious meth-, ods'of wire winding a-pipe where the load which caused JPatented June 5, 1956 3 the tension has had to act over the entirelength of the wire.

Referring now to the drawings in detail, Figures 1, 2 and 3 show themanner by which the pipe 21 is wound or wrapped with tensioned wire 20.The wire is first presented to drum 22 where it is wound thereon severalturns as indicated at 25. The wire is then passed over wheels 26 and 27and Wound on pipe 21. Wheel 27 is mounted on a threaded shaft 28 whichis rotated by means not shown to advance the wire 20 during the windingoperation. The drum 22 and pipe 21 are mounted co axially on shaft 23.Power is supplied by means of motor 24 to drive shaft 23.

The drum 22 acts as a torque regulating device to provide slippage whenthe tension on wire 20 is excessive. This will enable the wire to bewound on the pipe at constant tension.

It will be understood from the above discussion that a torque regulatingdevice is theoretically not necessary.

However, in practice it has been found difiicult to attain thetheoretical size of the drum to produce the proper stress.

This is readily apparent when it is considered that both the diameter ofthe drum and pipe must be maintained I absolutely constant in order toproperly stress the wire.

In practice it is difficult to maintain the exact working ratios betweenthe drum and pipe due to several factors. For example, the pipe may varyin diameter as in the case of a bell end pipe or creep of the wirearound the drum may result in the wire being too loose, with attendantlow stress when applied to the pipe.

Accordingly, this practical difiiculty is overcome by selecting a drumof smaller diameter than is necessary to properly stress the wire. Thiswill result in the wire being overstressed. A torque regulating deviceis employed with the drum to permit slippage thereof to relieve theoverstress in the wire to the desired point. By this arrangement it ispossible to select a drum size which would normally overstress the wireto or over the breaking point. The torque regulating device would, underthis condition, permit the drum to slip relative to the pipe therebyrelieving the overstress. Consequently, a drum of small enough diametercan be used with a variety of pipe diameters. The drum operates tostress the wire beyond the proper stress and the torque regulatingdevice serves to assure constant tension on the payed out wire to theproper degree.

The torque regulating device can be any suitable apparatus that willfunction as desired. It has been found that a brake is suitable for thispurpose. While any of the well known types of brakes can be used as acontrollable torque device to provide slippage to dissipate any desiredportion of the power, the most common types are the mechanical dryfriction type, the fluid coupling type, the magnetic-fluid type, theelectromagnetic and electrostatic clutch. Of the above types of brakesthe mechanical dry friction and magnetic fluid types are preferred. Asshown in the drawings, Figures 2 and 3, the drum 22 is provided with amechanical dry friction clutch which is designed to slip continuouslywith very dependable torque controlling characteristics to reduce theoverstressed wire to a constant tension with the desired stress. As withany dry clutch, its static friction is greater than its moving frictiou.Therefore, in order to prevent chattering, the clutch is operated toslip at least several R. P. M. under normal operating conditions tobring it into the range of dynamic friction. As the slippage is keptsmall, the power dissipation is correspondingly small and hence theoverall load is not appreciably increased.

Figures 5, 6 and 7 show a modified form of this invention. The pipe 30to be wire wound is mounted on rubber rollers 31 and turned thereon. Theweight of the pipe on the rollers develops sufficient friction so thatthe pipe may be turned by the rollers against the pull of tcnsioncd wire32. Offset from the pipe and running laterally there to is a splinedshaft 33. Carried thereon is a tapered brake drum 34 which is free toslide longitudinally along the splined shaft 33 but engages the splinesso that the drum and shaft can rotate as a unit. A motor supplies thesmall force necessary to drive the pipe 30 and drum 34. The motor 35rotates the splined shaft 33 which causes the pipe 39 to turn by meansof a chain drive consisting of sprockets and 46 and chain 47.

In order to advance the wire 32 during the winding operation and tosupport the splined shaft 33, a rail or beam 36 of considerable rigidityis mounted beneath the splined shaft 33 so that the axes of the shaftand rail are substantially parallel. The drum 34 is mounted with acarriage 37 which rolls on the rail 36 by means of wheels 38. Passingthrough the carriage 37 and fixed nuts 40 is a threaded shaft 39 wherebythe traversing of the drum is effected. This shaft 39 is rotated bymeans of motor 35 and a chain drive from the shaft 33 consisting ofsprockets 42 and 43 and chain 44. As can be seen the rate at which wirewill be payed out from drum 34 will be less than the take up rate of thepipe 30. This will impart a stress to wire 32. The relative diameters ofthe drum and pipe are such that wire 32 will be overstressed; a clutchsimilar to that shown in Figures 2 and 3 is contained within drum 34 andserves to relieve the overstress and maintain the tension on wire to aconstant degree.

In Figure 8 is shown a scheme for winding pipe vertically. The pipe tobe wound is placed vertically upon a turntable 51 which is mounted in apit 52 in timber flooring 53 by means of a centering pin 54. On theturntable 51 is a sprocket 55. Located beneath the turntable 51 areturntable rollers 56. A chain drive is provided to supply power to turnthe pipe 50 and it consists of sprocket 55, sprocket 58, and a chain 59linking the two sprockets together. A speed changer 60 is mounted abovesprocket 58 and the two are connected by a vertical shaft 61. Ahorizontal input shaft (not shown) extends from the speed changer 60upon which is mounted a tapered drum 62 provided with a brake assemblysimilar to that shown in Figures 2 and 3. Power is supplied to turn thedrum 62 and pipe 50 through the input shaft to the speed changer 60. Awire roll 63 on a swift 67 is suitably mounted to pay wire 64 to thetapered drum 62 and through guide rollers 65 to pipe 50 where it iswound. The guide rollers 65 are mounted on a screw traversing mechanism66 in order to evenly feed the wire 64 along the length of the pipe 50.Consequently, as the various parts are so chosen as to effectively takeup and wind the wire 64 on pipe 50 faster than it is payed out by drum62, the wire 64 will be stressed. Also as the directions of rotation arepre-selected in accordance with the discussion in conjunction withFigures 1 and 4, the winding is carried out with the minimum expenditureof power. The wire 64 is normally overstressed by drum 62 and pipe 50.Therefore a clutch relieves the overstress and keeps the tension on thewire constant.

A method and apparatus for producing a stress in wire when winding on atank with a low-power consumption is shown in Figures 9 and 10. A rollerchain 70 is placed in frictional engagement with the face 71 of a tankwall 72. The chain 70 also meshes with a drive sprocket 73 located on atruck frame 74 provided with rear wheels 75 on axle 77 and a front wheel76. The sprocket 73 is mounted on a shaft 78 which is driven by a motor79. Also mounted on the shaft 78 is a tapered drum 80 containing aclutch assembly similar to that shown in Figures 2 and 3. Also mountedon a shaft 81 projecting from frame 74 is a wire roll 82 on a swift 83.The wire 84 is payed out from the roll 82 and passes several turnsaround the tapered drum 80 and then wrapped around the tank wall 72.Since the drive sprocket 73 is of greater diameter than the drum 80, therate of linear forward movement of the truck relative to the wall willexceed the linear rate that wire 84 is payed out from drum 80;consequently, the wire will be stressed during the winding.

The manner by which multiple wire linear stressing can be accomplishedfor a roadbed, airstrip, beam or the like is shown in Figures 11 and 12.A car 90, provided with flanged wheels 91 on axles 98, rides on rails 92which straddle the road surface or the like to be paved. The car 90 hasa frame 93 which forms a platform 94. On the platform 94 are a series ofwire rolls 95 each mounted on a swift 96. On the ends of a horizontalshaft 97 located centrally of the car 90 are driven sprockets 99.

Chains 100 mesh with the drive sprockets 99. One end 105 of the chains100 is dead-ended at a distant point ahead of the car 90. The other end101 of the chains 100 is connected to a tractor, winch, or othersuitable device. The wire 102 on swift 96 passes between a pair ofrollers 103 for initial braking, then several turns around a tapereddrum 104 mounted on shaft 97 and finally is payed out onto the roadbed.The drum 104 is provided with a brake assembly similar to that describedin conjunction with Figures 2 and 3. A drum 104 and a pair of rollers103 are provided for each wire roll 95. Inasmuch as the drive sprockets99 are of greater diameter than the drums 104, the wire 102 will bepayed out at a slower rate than the rate of forward motion of car 90when end 101 of chain 100 is pulled or take up of wire by the road.Consequently, the Wire 102 will be stressed during its pay-out. As thesprocket and drum tend to normally overstress the wire, the brake indrum 80 will permit it to slip and thereby relieve the overstress andmaintain the tension on wire 102 to a constant degree.

In each of the assemblies shown in Figures 1, 5 and 8-10 inclusive thewire leading to the tapered drum is provided with a small initial backtension by any suitable means as explained with reference to Figures 1and 4 for the purpose of preventing the wire from slippinguncontrollably around the tapered pay-out drum.

The tapered drum is the preferred form of a pay-out device. Howeversimilar devices may be employed depending upon the wire to be payed out.By way of example, in the case of paying out flat wire a tapered drumwould be unsatisfactory and it would be necessary to use a conventionalpay-out device for flat wire.

Although this invention has been shown in specific embodiments, it isnevertheless understood that various changes and modifications obviousto one skilled in the art may be made without departing from the spiritand scope of this invention.

I claim:

1. Apparatus for continuously prestressing a concrete pipe comprisingsupport means to hold a concrete pipe for rotation, a shaft, a drumrotatably mounted on said shaft, drive means connected to drive saidshaft and said support means to rotate the concrete pipe, a source ofwire, said wire leading from said source, being wrapped several turnsaround said drum and then being anchored to the concrete pipe, said drumhaving a diameter less than the diameter of the concrete pipe so thatthe wire is payedout from said drum at a rate less than the rate of wiretake-up by the concrete pipe such that the wire tends to be excessivelyoverstressed, and a slipping clutch located within the drum anddrivingly connecting said shaft and said drum to enable said drum toslip relative to said shaft to reduce the stress of the wire to apredetermined value.

2. Apparatus for continuously prestressing a concrete pipe as defined inclaim 1 wherein said support means is a rotatably mounted turntable.

3. Apparatus for continuously prestressing a concrete pipe as defined inclaim 1 wherein said support means includes two pairs of rollers withone roller connected to be rotated by said drive means.

4. Apparatus for continuously prestressing a concrete pipe as defined inclaim 1 wherein said drum and the concrete pipe are coaxially supportedon a common shaft with the concrete pipe fixed to rotate with saidcommon shaft and said drive means is connected to rotate said commonshaft.

References Cited in the file of this patent UNITED STATES PATENTS1,180,232 Brown Apr, 18, 1916 1,249,809 Noble Dec. 11, 1917 2,175,479Miller et al Oct. 10, 1939 2,215,361 Miller et a1 Sept. 17, 19402,498,681 Hirsh Feb. 28, 1950 2,573,793 Kennison Nov. 6, 1951

